Cloud Atlas by David Mitchell was a very complex, spectacularly well written novel that I admired, liked, and was frustrated by. If you haven't read the book, the six plot lines across five or six hundred years is going to be a surprise. The book structure has the oldest story start first. It's then interrupted by the second story, which is interrupted by the third, on up to the sixth. The sixth story completes, then the fifth, the fourth, and so on back to the first. Lana and Andy Wachowski and Tom Tykwer decided to mix all six together in rapid succession, with pieces of each time period averaging about four minutes(?) each, going as low as a minute, with dialogue or voice-overs often stretching into the next segment. I guess they decided that this structure would be easier to parse in a movie - I think they're right. However, that doesn't mean it's easy to parse, just easier.
It's been a while since I read the book, but the movie does seem to be an accurate interpretation (excepting the structural changes). I do remember the frustration of reading the book, and it somehow feels appropriate that the movie was equally frustrating - like many of the Wachowski's products. It has moments of transcendence, but it's also kind of a mess in places.
And what the hell is it about? Connection: connecting to other people, trusting and supporting them. And the necessity of following your conscience and doing good, for without this the world fails. That makes it sound preachy: happily Mitchell and the Wachowskis and Tykwer make more subtle and compelling arguments.